1. Field of the Invention
The present invention relates to a technique for reproducing dynamic images from compression coded image data. In particular, the present invention relates to a method and apparatus for displaying picture frames using single field data contained in two-field image data, for example, in image data encoded by the MPEG-2 (Moving Picture Experts Group 2) standard.
2. Background Art
Scanning methods of dynamic images mainly consist of two types of methods, that is, sequential scanning and interlace scanning. In the sequential scanning method, data of all pixels in each frame are obtained at the same moment. In contrast, in the interlace scanning method, data of pixels in even-numbered and odd-numbered scanning lines in each frame are obtained at different moments. Compression of dynamic images according to the MPEG-2 (Moving Picture Experts Group 2) standard supports both the sequential scanning and the interlace scanning.
However, in the case where interlaced dynamic image data scanned by the MPEG-2 system is reproduced by a computer system, because the CRT display displays the interlace scanned dynamic images by sequential scanning, the dislocation of pictures in the two fields which form each frame deteriorates the quality of the dynamic image.
In order to prevent the deterioration of the quality of dynamic images in such a case, various techniques have been proposed for transforming interlacedly scanned dynamic data to dynamic image data suitable for the sequentially scanning display. For example, in the line interpolation method, data of one field is copied to the other field in the same frame, and each line in the first field is displayed twice in the manner of the sequential scanning. In the linear interpolation method, averages of each of the neighboring lines are taken, and each line in one of the fields and the averaged line are alternatively displayed in the manner of sequential scanning. In another method, after the mobility of the image between the two fields is calculated, the linear interpolation method is applied when the mobility is large, and the line interpolation method is applied when the mobility is small.
However, both the line interpolation method and the linear interpolation method have the drawback that the definition of dynamic images is reduced and images become indistinct. Furthermore, the third method requires high calculation speed for calculating the mobility of the image, and has the drawback of burdening the computer system.